Head-mounted rear-view!
"A cyclist, in order to view what is behind them has to turn much the same 160-170 or so degrees to focus on anything behind them."
NO THEY DO NOT. There are several designs of rear-view mirror that clip onto your helmet or sunglasses. They provide an excellent view behind, and only small motions of the head are needed to aim the view where you need it.
I commute daily with one, and road-skated for years with them. Total game-changer, no head-turning needed! I don't know why more riders don't use them, unless it's the ten grams of weight or their mates' stupid comments.